Induction of apoptosis by mifepristone and tamoxifen in human LNCaP prostate cancer cells in culture

BACKGROUND. Published data indicate that antiprogestins and antiestrogens c ould inhibit prostate cancer cell growth in vitro and in vivo. The main obj ective of the present studies was to explore the role of bcl(2) and TGF bet a(1) for induction of apoptosis in LNCaP prostate cancer cells growing in c ulture as a treatment response to the antiprogestin, mifepristone, and the antiestrogen, 4-hydroxytamoxifen. METHODS. In vitro cell viability (cytotoxicity), DNA fragmentation, and cha nges in the expression of bcl(2) and TGF beta(1) proteins were assessed usi ng the sulforhodamine B protein dye-binding assay, specific ELISA, and comp etitive inhibition assays. RESULTS. Both steroid antagonists induced a significant time- and dose-depe ndent cell growth inhibition (cytotoxicity). This inhibition of viable cell s was associated with a significant increase in DNA fragmentation (apoptosi s), downregulation of bcl(2), and induction of TGF beta(1), protein. Abroga tion of the mifepristone- and 4-hydroxytamoxifen-induced cytotoxicity by TG F beta(1)-neutralizing antibody and by the addition of mannose-6-phosphate confirmed the correlation between induction of active TGF beta(1) and subse quent prostate cancer cell death. The effect of mifepristone was not signif icantly reduced or prevented by occupying the progesterone or glucocorticoi d receptors by their corresponding high-affinity native ligands. On the con trary, the effect of a combination of mifepristone with progesterone or hyd rocortisone on the increase in DNA fragmentation, bcl(2) downregulation, an d induction of TGF beta(1) protein was additive and significantly different (P < 0.05) from the effect of mifepristone monotherapy. CONCLUSIONS. Our data suggest that mifepristone and tamoxifen are effective inducers of apoptosis and may represent nonandrogen-ablation, novel therap eutic approaches to over-come a potential intrinsic apoptosis resistance of androgen-independent prostate cancer cells. Prostate 43:31-42, 2000. (C) 2 000 Wiley-Liss, Inc.